Gerald O. Davis, PE,
President and co-owner of DM&ME, has over 40 years experience in Metallic materials Usage, Corrosion, Metallurgy, Mechanical Failure, & Root-Cause Failure Analysis
. His recent background includes work as a corrosion researcher, senior engineer and program manager for Battelle Memorial Institute, DNV, Inc., Henkels & McCoy, Inc., respectively and, since 2004, for DM&ME as an independent consultant. For (7) years he served as a mechanical engineer and maintenance/reliability engineer in a continuously operating chemical processing plant.
Mr. Davis provides services to a variety of industrial clients who desire outside help in his knowledge areas. Clients include those interested in targeted materials selection, prevention of equipment failure, or on-site short-course training for materials matters. Located in Central Virginia, he provides services across the nation.
Consulting Services Include
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- Metallurgical Root-Cause Failure Analysis and Consulting
- Metallic Materials Selection & Design Reviews
- Corrosion Analysis and Control
- Mechanical Failure Analysis
- Customized On-Site Materials Training
Sometimes the physical properties of hardness and hardenability are confused. Hardness represents an existing condition after processing by heat treatment. It is a direct indicator of the mechanical strength of the steel. Hardenability denotes the potential of a steel to develop a particular value of hardness after a particular heat treatment. Hardenability is primarily dependent on the chemical composition of the steel. Hardenability is associated with a steel's ability to develop hardness to a given desired depth in thickness of the finished product. Developing high hardness throughout thick cross sections is usually more difficult to attain without adding expensive elements (compared to carbon) to the composition.
Many considerations are included in a valid engineering design process. Typically decisions that provide for safe service and expected reliability in the given component or structure are the most critical. Determining the numerical value of an appropriate safety factor (or factor of safety) during design is vital to achieving mechanical or structural integrity.
A common cause of failures in various types of equipment is fatigue failure of bolts that secure parts together. Fatigue in any type of dynamically loaded mechanical component accounts for more than 80% of all failures. This post reviews some important factors in fatigue failure of metallic bolts.
The working relationship between the attorney and their expert witness in a case can be more effective if a few simple guidelines are followed. These are common sense things but one or more can be overlooked in the frequent day-to-day rush that busy attorneys face. When that happens some of the potential contributions from the expert may be compromised or lost to the detriment of the attorney's client.
Too frequently an attorney will begin to seek a potential expert witness only after having done considerable initial work. Often there is a last minute rush to locate and select specialized technical assistance. These approaches can have expensive consequences. Alternatively, securing a suitable expert early in the litigation process offers the following advantages for the retaining attorney:
Many negative consequences can result from failures of a range of different products that often lead to property & casualty insurance disputes or product liability legal actions. The products may include consumer or industrial goods. Typically the private user or worker is injured or a business incurs significant financial loss. The injured individual, insurance carrier, attorney(s) or industrial manufacturer and user are all interested to confirm what went wrong – and who is liable. Resolution often depends on engineering analysis.
Clearly it is advantageous to know when corrosion is occurring in operating equipment to avoid future failure. There is extensive literature on this topic. This post is a brief summary of information selected from the four references cited below. Each source includes several other references.
"3D printing" or the more descriptive term - additive manufacturing (AM) - has received much publicity in recent years. What is this technology and what are some of its practical features? This blog is a summary of AM and its on-going development to make actual service components using metal alloys. Presented are selected portions of information provided in the two references cited.
Most engineers know about the danger of galvanic corrosion caused by physical contact between dissimilar metals exposed to a corrosive liquid. However, this possibility is often overlooked and other features of this type of corrosion may not be widely known.
It is essential when beginning a root-cause failure analysis involving metallic materials to collect and maintain the as-found physical evidence properly prior to detailed examinations. This has two objectives. In all cases collecting and protecting the evidence in its undisturbed condition provides the best opportunity to derive meaningful good results from the subsequent analyses. Secondly, in a legal proceeding lack of attention to these matters can produce the accusation of spoilation of evidence. As a minimum this will cause presentation problems for the offending party in the suit. At worst such deficiencies by that party may cause the case to be thrown out.
Aluminum alloy materials are well known for their light weight and strength-to-weight ratios. They are also susceptible to several forms of corrosion. Relative to other metals, their natural electrochemical potential places them adjacent to other very susceptible (active) metals such as magnesium (Mg) and zinc (Zn) in a traditional galvanic series in seawater. However, Al alloys naturally form a very thin, protective (passive) oxide film on their surface when exposed to oxygen. This film prevents corrosion as long as it is maintained over the surface. Pitting corrosion is a common form of attack on aluminum. This is typically caused by exposure to halide ions, chloride ions being the most common type found in corrosive media, that breakdown the passive film at discreet spots. This permits pits to initiate and grow.
Often when engineers consider mechanical fatigue they envision cyclic, reversing stresses in a spinning shaft or possibly the up and down flex of aircraft wings. Rolling contact fatigue (RCF) or the associated mechanical wear is an important, closely related process to the traditional mechanism of fatigue but with distinct differences. RCF is also often known as spalling.
This term raises some vital issues that the engineer should be aware of when using it. First several definitions are available and thus it is perceived differently by different groups and individuals. From a legal standpoint, in many states, using the term to describe a product that was involved in an incident involving an injury means that the designer or manufacturer of that product may be financially liable for the injury. Engineers sometimes use the term simply to indicate an imperfection in a product without intending its frequent legal use. Further the engineer realizes that no material and no finished product is perfect. However, these variations from perfection do not necessarily mean they were cause for failure and thus the injury that may occur in a given incident. Some product liability attorneys may not readily acknowledge or understand this distinction.
The optimal time to make decisions and take actions to minimize potential failures of equipment, facilities and components is during their design. This two-part blog post provides an overview of the types of issues involved and specific actions that can be useful to the design engineer. Archived blog posts (at www.dmme-engineering.com) that discuss specifics are provided parenthetically.
Four, tri-lobe pumps were damaged and required extensive repair during the latter stages of construction for a modification in a pharmaceutical manufacturing plant. The economic loss was significant and the general contractor for the work paid the plant's owner for the loss. The renovated units were installed and are in use. However, the general contractor then sued one of its subcontractors - a welding contractor that fabricated and completed weld joints between piping sections on the inlet side of the pumps. The general contractor claimed poor quality welds in the piping permitted loosened weld fragments to enter the pumps during the required water flow verification of the system and this caused the damage.
Most realize that damage due to corrosion of metals is costly - but what specifically is that cost and what is included in the total? A study completed in 2002 sponsored by the Federal Highway Administration (FHWA), the National Association of Corrosion Engineers (NACE International) and implemented by CC Technologies Laboratories (now part of DVN) addressed those questions.
Material selection entails picking an engineering material - either metal alloy or non-metal - that is inherently resistant to the particular corrosive environment and also meets other criteria. Variables that will affect corrosion are established along with materials that may provide suitable resistance for those conditions. Obviously other requirements such as cost and mechanical properties of the potential materials must be considered.
Pin-hole leaks from a fire-control sprinkler piping system just above the false ceiling of multiple rooms in an office building resulted in a suit against three parties involved with supplying the system. The plaintiff - a financial service organization that owned the building - had much computerized transaction data stored on magnetic tapes in several rooms damaged or destroyed by the incident. The monetary loss was major. The leaks occurred within two years after the system was installed. This period is clearly far short of the expected life of the system. Defendants in the case included the supplier of the piping used in the system, the engineering firm that designed it and the installation contractor.
A variety of low-voltage electronic devices may fail to operate properly because of exposure to certain corrosive, gaseous environments. Susceptible items include consumer products such as microwave ovens, audio equipment, TV's and personal computers as well as many types of industrial sensors and automatic control devices. Failure generally occurs because of specific application factors. These include the severity of the environment, the presence or absence of atmospheric sealing of components within the device and the metals used at critical internal locations. Frequently complete failure doesn't occur but normal operation is erratic.
A full size, cylindrical tank trailer pulled by a truck tractor/ cab split open on its lower section at mid-span and released hundreds of gallons of hydrochloric acid (HCl) onto a secondary highway in a northeastern state. When this occurred the truck driver jumped out of the truck's cab and sustained acid burns to his ankles because he was wearing low-quarter shoes.
A severe personal injury incident occurred as a recreational fishing boat was approaching a dock at approximately 20 mph after a day on the water. The large outboard engine (75 HP) on the stern of the boat struck a fixed underwater obstruction, flipped into the boat while still running and amputated the hand of a passenger seated near the engine.
A licensed professional engineer (P.E.) is required to adhere to a Code of Ethics for Engineers in all work he undertakes. However, there are some special criteria when employed as an expert witness.